Hematopoietic cell-supported therapy is employed for a broad spectrum of malignancies and hematological disease. However, the approach is limited by the availability of hematopoietic stem cells; thus, the possibility of expanding the number of hematopoietic stem and progenitor cells is a critical issue for a number of therapeutic strategies. Recently, we discovered that nitric oxide (NO) is an important endogenous regulator of hematopoietic stem cells. We found that it is possible to expand the pool of hematopoietic stem cells in the bone marrow by suppressing production of NO with systemically administered inhibitors of NO synthase (NOS) activity. In this proposal we will investigate whether ANO-1020 (NG-methyI-L-arginine or L-NMMA), a potent inhibitor of NO biosynthesis developed by ArgiNOx, can be used to expand hematopoietic stem cells in the bone marrow and to increase neutrophil content in the peripheral blood. ANO-1020 is the only NOS inhibitor that has undergone FDA-approved, physician- and industry-sponsored Phase II clinical trials and found to be well tolerated and safe. We will use a mouse model to determine the efficacy of ANO-1020 in a) expanding hematopoietic stem and progenitor cells in two experimental settings (with and without bone marrow transplantation), and b) expanding the number of neutrophils in the blood after bone marrow transplantation. Clear and measurable milestones are proposed that will define success and will determine the transition to the SBIR Phase II studies. The proposed use of NOS inhibitors for stem cell expansion is protected by issued US patens and foreign counterparts that are exclusively licensed to ArgiNOx. If successful, these studies will have a major impact on the clinical strategies to combat hematological disorders and cancer.